In what was arguably one of the most anticipated rock n' roll reunions in years, Axl Rose, Slash and Duff McKagan teamed up for their second performance together since 1993 (they put on their first official reunion show two weeks ago in Los Angeles).

Twilight actor Kellan Lutz was just one of the many celebrities who watched the band perform some of their classic hits like "Sweet Child O' Mine," "Paradise City" and "Welcome to the Jungle."

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And he wasn't the only one in the crowd rocking a GNR T-shirt! Victoria's Secret model Alessandra Ambrosio was clad in a band tee, which she paired with an edgy leather jacket, denim cut-offs and tan ankle booties.

Halfway through the set, Rose brought out AC/DC's lead guitarist, Angus Young, to the stage to perform a few classic hits from the Australian rock band, including "Riff Raff" and "Whole Lotta Rosie."

The band announced on Saturday that Rose will be joining AC/DC on the remaining dates of their Rock or Bust world tour, replacing frontman Brian Johnson, who is reportedly leaving the band due to hearing issues.

"AC/DC band members would like to thank Brian Johnson for his contributions and dedication to the band throughout the years," a statement from AC/DC read. "We wish him all the best with his hearing issues and future ventures. As much as we want this tour to end as it started, we understand, respect and support Brian's decision to stop touring and save his hearing. We are dedicated to fulfilling the remainder of our touring commitments to everyone that has supported us over the years, and are fortunate that Axl Rose has kindly offered his support to help us fulfill this commitment."

This won't affect Rose's upcoming Guns N' Roses Not In This Lifetime tour gig, however, as Rock or Bust wraps June 12 in Aarhus, Denmark. Rose will then head to Detroit, Michigan, on June 23 to kick off GNR's summer tour.

Young's unannounced appearance wasn't the only surprise on Saturday, however. During Zedd's set, Kesha took the stage to deliver a powerful performance of the EDM producer's "True Colors" track.